Hydrofluoroolefins (HFOs), such as tetrafluoropropenes (including 2,3,3,3-tetrafluoropropene (HFO-1234yf), are now known to be effective refrigerants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilants carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids, chemical intermediates, monomers and the like. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFOs do not contain chlorine and, thus, pose no threat to the ozone layer. HFO-1234yf has also been shown to be a low global warming compound with low toxicity and, hence, can meet increasingly stringent requirements for refrigerants in mobile air conditioning. Accordingly, compositions containing HFO-1234yf are among the materials being developed for use in many of the aforementioned applications.
Some HFOs are prepared by multiple steps that involve fluorinating a chlorinated organic compound with a fluorination agent such as hydrogen fluoride in the presence of a fluorination catalyst. These reactions may be conducted in either the liquid or gas phase or a combination of these. In one process to manufacture HFO-1234yf (2,3,3,3-tetrafluoropropene), the following reaction sequence is known:Step 1: TCP+3HF→1233xf+3HClwherein TCP (also known as 1230xa) is 1,1,2,3-tetrachloropropene, or CCl2═CClCH2Cl; and 1233xf is 2-chloro-3,3,3,-trifluoropropene, or CH2═CClCF3. Step (1) preferably occurs in the vapor phase reactor charged with a solid catalyst, preferably a fluorination catalyst, e.g. chromium oxide (Cr2O3) and the like as known in the art.Step 2: 1233xf+HF→244bbwherein 244bb is 2-chloro-1,1,1,2-tetrafluoropropane, or CH3CClFCF3. Step (2) preferably occurs in a liquid phase reactor charged with a liquid catalyst. A by-product of Step 2 can also form as follows: 1233xf+2HF→245cb+HCl, where 245cb is 1,1,1,2,2-pentafluoropropane, or CH3CF2CF3;Step 3: 244bb→1234yf+HClwherein 1234yf is 2,3,3,3-tetrafluoropropene, or CH2═CFCF3. Step (3) preferably occurs in a vapor phase reactor with a dehydrochlorination catalyst.
It has been found that while the catalyst used in Step (1) is quite active and selective, it nonetheless tends to deactivate (lose activity), slowly during the reaction. Among other things, it has been theorized that often in the course of known protocols, when TCP is heated and vaporized (including preferably in the presence of anhydrous hydrogen fluoride (AHF)) undesired reactions occur. It is believed these include the formation of oligomers, polymers, and decomposition products (C1 and C2 carbon-containing compounds) which can further lead to coking of the catalyst. Thus, formation of these compounds is thought to lead directly to catalyst deactivation. Deactivation of the catalyst compromises yield and creates other economic disadvantages and disruption to the process.
Therefore, a need exists to extend catalyst life for the conversion of 1230xa to 1233xf.